People really need to stop always quoting Joel - he is not a definitive go-to software spokesperson, and has some very strong (and often wrong) opinions about things -- shaped by years at Microsoft doing things only the Microsoft way.
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He is puffing his product in this blog post -- nothing more.
Well, Docker just slapped a "1.0" sticker on and called itself "production ready" when it clearly wasn't (features like in this 1.2 release are kind of mandatory for any serious deployments).